Page 181 - Materials Chemistry, Second Edition

164 Practical Design Calculations for Groundwater and Soil Remediation

If no pilot tests are conducted, an estimate could be made based on previous
experiences. The R values ranging from 30 ft (9 m) to 100 ft (30 m) are reported
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in the literature, and typical pressures in the extraction wells range from 0.90
to 0.95 atm [3]. Shallower wells, less permeable subsurface, and lower applied
vacuum in the extraction well generally correspond to smaller R values.
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Example 5.7: Determine the Radius of Influence of a Soil-Venting
Well by Using the Pressure Drawdown Data (Pressure
Data Are Given in the Atmospheric Unit)
Determine the radius of influence of a soil-venting well using the following
information:

• Pressure at the extraction well = 0.9 atm
• Pressure at a monitoring well 30 ft away from the venting well = 0.98
atm
• Diameter of the venting well = 4 in.

Solution:
(a) Let us define the R as the location where P is equal to the atmo-
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spheric pressure. The R can be found by using Equation (5.3) as:
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rR )
2
P r − P w ( P RI − P w) ln(/ w
2
2
2
=
RR )
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ln(/ w
ln[30/(2/12)]
2
2
2
2
(0.98) − (0.9) = (1.0 − 0.9 )
ln[/(2/12)]
R I
R = 118 ft
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(b) For comparison, let us now define the R as the location where
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the drawdown is equal to 1% of the vacuum in the extraction
well:
The vacuum in the extraction well = 1 − 0.9 = 0.1 atm
Thus, P = 1 − (0.1)(1%) = 0.999 atm
RI
ln[30/(2/12)]
2
2
(0.98) − (0.9) = (0.999 − 0.9 )
2
2
R I
ln[/(2/12)]
R = 110 ft
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Discussion:
The R value from part (b), 110 ft, is about 7% smaller than that from
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part (a).